Experimenting with crank length

[Jim Thill - Hiawatha Cyclery]

Not exactly a Riv-specific topic, but I think some of you folks will find this interesting, and I'd appreciate any insight. Maybe Jan has done a study, or will do one soon.

Over the years, I've used cranks in 165, 170, and 175 mm lengths, and all seem to be ok. I think I prefer the shorter end of the range, 165 and 170 mm cranks (I'm just short of average height at 5'8"), but 175 works well enough. Anyway, it sort of blows my mind that with the wide variance in human sizes, and bikes and parts to address most of that variance, that the total difference from "short" to "long" in the crank world is only 10 mm. So if you're 6'5", you're supposed to ride 175. If you're 5'9" you maybe ride 170. If you're 5'2", obviously, you'd ride 165. My point here is that it's ludicrous that a teeny-tiny 5 mm change in crank length could account for, say, 6-8" in overall body height. It's doubly ludicrous that a person can easily have, for example, 25-50 mm of saddle fore-aft adjustment (with different saddles/seatposts) on any given frame, but only 5-10 mm to be gained or lost switching cranks. It's a tough subject to discuss without anecdotal bias because if you're somewhat close to average, you probably do ok with whatever you're riding. If you're really tall, you could probably be riding 180, 190, or even 200 mm cranks with improved efficiency and ergonomics, but you've probably always been ok on 175. If you're really short, even a "short" 165 may put your knees and hips through the wringer on every pedal stroke. But we've all been forced to choose from these limited offerings, and obviously we're still pedaling, so it must be tolerable. Still, of all the ergonomic considerations on bikes, this is the only part that moves regularly, and repetitive motion injuries are no joke, so it makes sense to get it right, or closer to right.

My ladyfriend Abby is pretty short - 5'3" with shortish legs. She has a 46 cm LHT and a 14" Pugsley that fit her pretty well. She had to cut a tour short last summer because of knee pain and swelling after several days on her LHT. The cranks on the LHT at the time were 170 mm Deore with big ring replaced with bashguard, so crank gearing was 24/36/bash. After the trip and the knee issues, I set her up with some 152 mm Sugino XD (same gearing as before) that QBP sells and went as narrow on the BB as possible. So far the shorter, narrower crank seems like a winner, but she hasn't really put it to a serious test yet. My hunch is that better ergonomics equals better speed/efficiency, even if she loses a little theoretical leverage with shorter cranks. Time will tell.

But now I'm going to shorten a crank for her Pugsley (hard to find a stock pug-compatible crank under 170 mm). Since I'm not relying on a commercially available crankarm length, I decided to think about it a little more deeply. Tonight I drew a crude picture of some triangles and levers and pivots that represent the leg-to-crank/pedal relationship, and I took "Knee Over Pedal Spindle" (KOPS) as a goal for my analysis. KOPS has some known flaws, but it's close enough for my purposes. Then I started putting all the trigonometry into a spreadsheet, varying everything at different saddle heights and seat tube angles, solving for crank length, and taking the results with a big grain of salt (margin of error). In general, short legs and slack seat tubes mean cranks should be shorter. Longer legs and/or steeper seat tubes mean cranks should be longer. But much more impressive than that observation, is the range of crank lengths this predicts. If you're short, say 70 pbh, and you have a slack seat tube, you will probably do ok on 120 mm cranks. If you're riding comfortably on a 72 cm AHH, 200 mm arms would be more or less optimum if they don't drag on the ground. My computation shows that my own "optimum" is in the mid 160s for the seat tube angles I usually ride, which I know to be true from experience and perception (though not from a controlled scientific experiment). My ladyfriend should be on a 140 mm crank given her PBH and the 73deg ST on her Pugs. I should point out that these specific values are based on numerous wild-ass assumptions, and they should be understood to have a large margin of error. I wouldn't bet my life on any specific result. I would, however, wager that the range of optimal crank lengths is MUCH larger than what is widely available to us. I'd also suggest that tallies and shorties are not being well-served in this department.

Here in the Twin Cities we have this guy (friend of mine) who sells shortened cranks:
http://www.bikesmithdesign.com/

His page on cranks for children is perhaps inaccurately named, and provides some good general info about why a person would use short cranks.
http://www.bikesmithdesign.com/Short_Cranks/cranks4kids.html

In particular, for adults, he suggests crankarm length be at most 9.5% of height. For me at 5'8", this linear relationship suggests that I should be on 164 mm or shorter. Abby at 5'3" should be on 152 mm or shorter. Interesting.

[Garth]

Experimenting on myself, all "formulas" for crank length are bunk !   lol  lol    Yes, I said it !    I followed them , like "they" say, and I have found using shorter ones to be absolutely puuuurfect , for Me !   And yes .... I need please no one but me ... who else is there ?  lol 

I use Sugino XD 152's .  I have a 36" inseam and size 15 feet.  I use a mid foot position over the pedal ... another one of those "myths" I tested and debunked .  I get the speed of a short crank with the leverage of a long one with this way of riding ... and it came out by imagining it !!  What would it feel like to have the leverage of long cranks yet still be able to spin like short ones ?  Lo and behold ... this came to my mind to try and it's better than I even imagined !!!  

I could use even shorter ones, but these are fine for now as I am at the limits of bar height with my Bombadil already.
The 152 XD's come with 24/36/50 rings and are spaced as 7/8 speed.  Yes, the rings are spaced wider than the longer XD's.

[Kelly]

Garth,

You and I are on the same page .. it's bunk for me.  Then I am not as sensitive to bike setup as many.   I have 171 I think on the Ram and they are perfect.. those Rene Herse Cranks.. I have 175's on my AHH and 175's on my Bombadil with 172.5 on my Mountain bike....  I accidentally put 165's on a new build and didn't realize it till I was cleaning the bike a month later... I changed them out.. 165's really I'm 6'5" tall I can't ride those.. especially now that I know they are there.. :)

Kelly

[Bruce Herbitter]

I've tried 165, 170, and 172.5. Small changes can make a discernable difference on a bike. 170s work best for me (and I'm short with a 29" inseam) so that is what I stay with.

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[PATRICK MOORE]

And Garth, ever gnomic, uttered: "What would it feel like to have the leverage of long cranks yet still be able to spin like short ones ?  Lo and behold ... this came to my mind to try and it's better than I even imagined !!! "

O, unfathomable Garth: explain thyself to us of mere mortal ken: how, exactly, dost thou get long-crank leverage while you spin like short ones?

152s? Really? or was this an April Fools' joke that got held up?

Me, I found that 175s on a low gear were horribly annoying to spin and got rid of them. I use 170s, more or less, on everything.

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[Kenneth Stagg]

Small changes make a difference for me as well. 165's are sweet,
170's OK, 172.5's are hard for me to use. I've had occaision to
forget what length cranks were on a bike only to look down and wonder
just what was going on. Just me, though.

-Ken

[Eric Platt]

For some, the changes seem more important than others.  When first getting back into riding I was determined to have 175's because that's what I had before my layoff.  Since then, it's become less important.  Both the current Rivendells have 170's and feel just fine.  My LHT might have 175s on it.  But am not even sure at the moment. 

 

At least with my riding preferences, Q factor seems more important than crank arm length.  And there my preference is for wider.  The Shimano Alfine cranks seem about perfect, although will occasionally catch my right foot moving slightly outboard when riding. 

 

With Jim's original post, would assume the wider Q factor caused by the bottom bracket of a fat bike would then necessitate an even shorter crank with the feet further apart to get the same position as on a regular bike.

 

Eric Platt

St. Paul, MN

[Mike Schiller]

Another variable is femur length. It drives people to longer cranks and more seat setback  to get a good hip angle. With longer than average femurs (from bike fit sessions) a longer crankarm is a better match, at least for me.  I have 175's on all my bikes and prefer that for climbing. It may be because of my mountain bike background but 170's feel odd climbing. It's not something I notice spinning on the flats. 

... slightly above avg at ~6ft.

~mike

[Jim Thill - Hiawatha Cyclery]

I believe our perceptions are altered by the unnaturally narrow selection of crank options. In this world, 170 is the middle; 175 is long; and 165 is short. That is equivalent to mosf bikes being available in 55, 56, and 57 cm frame sizes. Something for everybody!

[Rambouilleting Utahn]

Very interesting observation and comments. I've often wondered if longer would be better for me. 

To make it more useful could posters include their PBH with their comments.

blissfully ignorant at 6' tall spinning on 175s with a 94cm PBH

[Leslie]

Bike A: 172.5 DuraAce triple crank on my Ram.
Bike B: 175 Sugino XD triple crank on my Bomba.

6'-tall, PHB of 87.6.

I think I'd prefer the 17.5, maybe even a 170, on the Bomba...

[Garth]

Well Patrick,   I was using 175's at the time and I started using a mid foot position over the pedal .   It felt wonderful but it also felt like I was using really looooong cranks !   I used to use 185's and this felt longer .  So that's when the short cranks came to mind.  I found some people used short cranks, and some people used a mid foot position, but no one combined them that I heard of  !  So .... why not me ? !!   It was love at first spin .... lol.   ahaahahahahah !!  It took a week or so to really dial in the saddle height, which was only about 5-7mm more than with the 175's because with a mid food position you lessen the overall reach to the pedal. It's just so fun to spin and have great leverage !   I noticed I was better using what power I do have, and after days of lots of climbs I was never sore-ish the next day like I would often feel before. Now of course .. all this is highly subjective to me ... but nonetheless it's wonderful :)


All I can say is try it.  start with a mid foot position on one of your bikes and play with it. (You have to lower the saddle a bit on a bike with your regular cranks) . It simply feels super efficient ... almost like more standing on the pedals but you're sitting, but not really(if that makes sense !).  All I can say is try it and you'll either experience it or not !!  Everyone has their way that works for them.

Oh, you need some flat bottomed shoes. Stiffer works better for this .. I use classic Birkenstock Arizona and Bostons. Chaco's would work well too, as would about "boat" style shoe .

[Deacon Patrick]

Colorado Patrick here. Riding barefoot I quickly learned midfoot is most comfortable and yes, the difference in power is astonishing. I actually took your post to mean what you describe below, and was puzzled when other's didn't follow. That should likely scare both of us! Grin.

With abandon,

Patrick

[René Sterental]

After years of foot pain, I finally discovered that the combination of flat wide and large pedals (DMR Vault - http://www.universalcycles.com/shopping/product_details.php?id=40265 in silver) and placing the foot on its middle over the pedals completely eliminated all the pain, provided the sole is somewhat stiff or above. On flexible sandals I still get some mild discomfort. So yes, the missing link all these years, even when I first tried flat pedals on my Riv bikes was the mid-foot position over the pedals. Otherwise, in my case, the pain comes right back!

 

That being said, I developed some pain on my inner hip, although not while riding. It was quite annoying, and I started switching to 172.5mm cranks from the 175 I was running on all my bikes (PBH 89, 5'11") since they allowed faster spinning and a bit less flexion at the hip, or so it felt to me. I have to say that this pain is mostly gone now, but it may be due to my improved eating habits (low carb/high fat) rather than to the change in crankset length. Nevertheless, I'm running now 172.5 on the Atlantis and Hunqapillar, and 175 on the Betty and my dual suspension MTB. Can't really tell them apart when I'm riding them so I'll see what happens.

 

René

[justin...@gmail.com]

I have noticed that when I pedal in the "sneaker position" (arch centered over pedal spindle) I feel like my cranks are longer too. I'm think that no matter what when the balls of our feet engage they go into the sprinters position. When the arch is flat on that's mostly impossible. This gives the feeling of a longer crank with a more solid connection. Hmmmm

-J, PHL, 171 - Saluki 165 - SimpleOne/Motobecane

[Nick Payne]

On 03/04/13 04:13, Jim Thill - Hiawatha Cyclery wrote:

I believe our perceptions are altered by the unnaturally narrow selection of crank options. In this world, 170 is the middle; 175 is long; and 165 is short. That is equivalent to mosf bikes being available in 55, 56, and 57 cm frame sizes. Something for everybody!

Leonard Zinn has a bit of a bee in his bonnet about crank length, and offers cranks in lengths from 130mm to 220mm: http://zinncycles.com/Zinn/index.php/components/custom-cranks.

According to his formula my optimal crank length should be 185mm. However, after almost 40 years of riding on 170mm cranks, and having almost a dozen bikes with that length of crank on them, I don't think I'll be bothering to change.

[Eric Daume]

I'm 6'3" and ride 175mm cranks, pretty much across the board. However, the other day when I was riding with my BMX pedals (ie, foot was free to wander on the pedal), I looked down to see my toes were about over the pedal spindle. At this point, wouldn't a shorter crank make sense? That's my latest thinking.

Eric Daume
Dublin, OH

[PATRICK MOORE]

I get it. I'll have to try that with my new Decksters -- well, try pedaling with my arch: I'm not going to swap out cranks. I loved the comfort of boat shoes with MKS touring pedals and straps, except that I kept pulling my shoes out of the pedals (or foot out of the shoes) so went to back to slottled ceats and then back to clipless as more comfortable.

I use SPDs or Looks on my bikes (the Decksters are for the SPDs) but move the cleats pretty far back, as I tend to sit way behind the bb and mash. I started, years ago, with saddle all the way forward and very high with a 120 rpm cruising spin. 

[hsmitham]

Well another great topic and one that applies to the well being of every cyclist as riding then having pain is counter productive. Thanks Jim! 

Now on to my non-scientific opinion, I'm 5' 101/2" with a PBH of 83.5 riding with a 170 mm crank arms. I used to ride exclusively with 172.5 cause that's what the industry seems to suggest for a 54 cm frame.

After reading Garth's thoughts I went for a ride and mid ride I moved my SPD cleats back effectively moving my mid foot over the pedal spindle, jumped back on the bike and started to pedal. Almost immediately I felt more power per stroke. The crank length felt like my old 172.5 mm crank arms, after a couple of miles I felt a nagging pain around my right hip, pulled over and lowered my saddle a mm or so and continued, hip pain gone! Road the rest of my ride this way and am amazed at the difference. I seem to be really sensitive to all the different angles, a little off and I feel it!  I rode today and felt a bit more muscle fatigue in my quads this is either because I'm a outta shape lump or the new angles related to the position change. I still think I need to dial in the saddle height and ride more miles so this experiment continues.

One last thing it seems to me that the longer the crank arm related to the individuals leg length the greater for an extreme on the up stroke and creating a need for more force on the down stroke this greater range of motion plus extra force would seem to me to add up to some orthopedic issues especially as one grows older as in my case. In my twenty's and thirties I could have ridden on 175's and never felt it. 

Musings from a mortal cyclist who wants as little pain as possible as is the case with Jim's significant person.

Hugh

Sunland, CA

[hsmitham]

Jim so interesting I was just thinking about crank arm length the other day! I suppose great minds think a like. Lol Really glad you brought this up.

Hugh

Sunland, CA

[Deacon Patrick]

I've taken a solid year to dial in my saddle height, tilt, front to back position etc. I make sure to only change one thing at a time and see how it goes for a 5+ hours of riding, including one ride of at least 3 hours, then shift as needed. WIth a mid-foot position on the peddles, I like my saddle lower (like many of you have described, and farther forward on the post. It's currently all the way forward, and my next "play" is to try it back from there slightly. It is amazing how the various adjustments interplay, with one shift leading to a re-adjustment of another that had been dialed in. Of course I'm only back to cycling for a year, after many years away, plus I have a very shallow learning curve not having memory, so hopefully you are faster at this than I am!

With abandon,

Patrick

[Garth]

That's Great Deacon Patrick !!!   Barefoot riding ..... that's pretty cool .  


   And Hugh, Yes ....it can take awhile to dial in your saddle height and fore/aft position, and of course some soreness my appear as your are changing and using slightly different proportions of muscles.  But all of this is the fun of exploring a different way of riding !!   It reminds me the only rules to cycling are those we set for ourselves :)   

I only wish I could change bars and stems as easily !  Hmmm..... maybe I can by using those cable breaker things, whatever they are called ?  Those devices that disconnect a cable in two ... what are those called, anyone ? 

[Garth]

I found my own answer ... lol..  Ritchey Quick disconnects is what they are !!!  For brake and derailer cables.

[Jim Thill - Hiawatha Cyclery]

Working with Mark Stonich (Bikesmith) the other night on a Dimension/Andel 175 mm mountain double crank I bought for this project, I came away with some 153 mm cranks for the ladyfriend. We'll see how it goes. For a lot of cycling enthusiasts, conditioned to the notion that 5 mm of crank length is a huge difference, 153 sounds ridiculously short. But they don't actually look weird. On a small bike, they look right. Proportional. Of course, looks can be deceiving, but my sense is that 153 mm is far from an "extreme" solution to a bike fit issue.

Incidentally, Mark S shortened some Sugino cranks for me a few years ago. In that case, the purpose was kid cranks for my tandem. I think they're 90 or 100 mm. So far, many miles have been happily pedaled on those cranks, by kids aged 3-7.

[Garth]

Yes ... 153 is not all that "radical" !   There are many triathletes that are using cranks as short as your kids !!!  No Joke .... and they wouldn't be doing it if it didn't work for them !!     You can get certain brands stock quite short, in a 110mm BCD.  Origin8 goes to 140mm and a few go down to the 120's. Of course, when you go that short you must consider having a large enough frame to be able to keep the bars raised !!    Triathletes don't have that issue of course . 

It's funny how long held beliefs about things can be changed in a heartbeat !!!!   That's the beauty of LIFE !!!!!!!